1. Field of the Invention
The present invention relates to a positive resist composition suitably used in the ultramicrolithography process of producing, for example, VLSI or high-capacity microchip or in other photofabrication processes. More specifically, the present invention relates to a positive resist composition capable of forming a highly refined pattern with use of electron beam, X-ray, EUV light or the like, that is, a positive resist composition suitably usable for fine processing of a semiconductor device, where electron beam, X-ray or EUV light (wavelength: around 13 nm) is used.
2. Background Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a resist composition has been conventionally performed. Recently, the integration degree of integrated circuits is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X ray or EUV light is proceeding.
In particular, the electron beam lithography is positioned as a pattern formation technique of the next generation or second next generation and a high-sensitivity and high-resolution positive resist is being demanded. In order to shorten the wafer processing time, the elevation of sensitivity is very important, but when higher elevation is sought for, not only reduction of resolution but also worsening of line edge roughness are brought about and development of a resist satisfying these properties at the same time is strongly demanded. The line edge roughness as used herein means that the edge of resist at the interface between the pattern and the substrate irregularly fluctuates in the direction perpendicular to the line direction due to the resist characteristics and when the pattern is viewed from right above, the edge gives an uneven appearance. This unevenness is transferred by the etching step using the resist as a mask and causes deterioration of electric characteristics, giving rise to decrease in the yield. Particularly, in the ultrafine region of 0.25 μm or less, the improvement of line edge roughness is a very important problem to be solved. The high sensitivity is in a trade-off relationship with high resolution, good pattern profile and good line edge roughness and it is very important how to satisfy these matters at the same time. Also, the image performance stability (in-vacuum PED) during standing after exposure in a vacuum is a very important performance when exposure is performed in a vacuum as done with electron beam, X-ray or EUV light. If the in-vacuum PED characteristics are bad, the performance greatly changes between initial stage and end stage of image-drawing at the time of drawing an image with electron beam or X-ray, as a result, the in-plane uniformity of the drawn pattern greatly fluctuates to cause serious decrease in the yield.
Furthermore, there is a problem that the above-described line edge roughness is also worsened during standing in a vacuum.
In the case of using EUV as a light source, the wavelength of light belongs to an extreme ultraviolet region and in corporation with a photochemical reaction such as negative conversion ascribable to EUV light, its high energy gives rise to a problem such as reduction of contrast. Therefore, also in the lithography using X-ray or EUV light, an important problem to be solved is to satisfy high sensitivity as well as high resolution and the like at the same time.
As for the resist suitable for the lithography process using electron beam, X-ray or EUV light, a chemical amplification-type resist utilizing an acid catalytic reaction is mainly used in view of high sensitivity and in the case of a positive resist, a chemical amplification-type resist composition mainly comprising an acid generator and a phenolic polymer which is insoluble or hardly soluble in an alkali developer but becomes soluble in an alkali developer under the action of an acid (hereinafter simply referred to as a “phenolic acid-decomposable resin”) is being effectively used.
With respect to the positive resist for use with electron beam, X-ray or EUV, some resist compositions containing a phenolic acid-decomposable resin have been heretofore known (see, for example, Patent Documents 1 to 6: JP-A-2002-323768 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-6-41221, Japanese Patent No. 3,173,368, JP-A-2000-122291, JP-A-2001-114825, JP-A-2001-206917).
However, it is failed at present by any combination of these compositions to satisfy all of high sensitivity, high resolution, good pattern profile, good line edge roughness and in-vacuum PED characteristics in an ultrafine region.